Zeta Cassiopeiae

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ζ Cassiopeiae
Cassiopeia constellation map.svg
ζ Cassiopeiae is found just south of the W asterism
Observation data
Epoch J2000      Equinox J2000
Constellation Cassiopeia
Right ascension 00h 36m 58.28419s[1]
Declination +53° 53′ 48.8673″[1]
Apparent magnitude (V) 3.66[2] (3.59 - 3.68[3])
Spectral type B2IV[4]
U−B color index –0.89[5]
B−V color index –0.19[5]
Variable type SPB[3]
Radial velocity (Rv)2.0[3] km/s
Proper motion (μ) RA: 17.38[1] mas/yr
Dec.: –9.86[1] mas/yr
Parallax (π)5.50 ± 0.16[1] mas
Distance590 ± 20 ly
(182 ± 5 pc)
Absolute magnitude (MV)–2.8[6]
Mass8.3[3] M
Radius5.9[3] R
Luminosity5,500[3] L
Surface gravity (log g)3.81[3] cgs
Temperature20,426[3] K
Metallicity [Fe/H]–0.23[7] dex
Rotational velocity (v sin i)17 ± 3[3] km/s
Other designations
Fulu, 17 Cassiopeiae, HR 153, HD 3360, BD+53°105, FK5 17, HIP 2920, SAO 21566, GC 727[8]
Database references

Zeta Cassiopeiae (ζ Cassiopeiae, abbreviated Zet Cas, ζ Cas), also named Fulu,[9] is a variable star[8] in the constellation of Cassiopeia. It has a blue-white hue and is classified as a B-type subgiant with an apparent magnitude of +3.66. Based upon parallax measurements, it is approximately 590 light-years from the Sun.


ζ Cassiopeiae (Latinised to Zeta Cassiopeiae) is the star's Bayer designation.

In Chinese astronomy, Zeta Cassiopeiae is called 附路, Pinyin: Fùlù, meaning Auxiliary Road, because this star is marking itself and standing alone in the Auxiliary Road asterism, Legs (mansion) (see : Chinese constellation).[10] 附路 (Fùlù) was westernized into Foo Loo, but that name was also designated for Eta Cassiopeiae by R.H. Allen, with the meaning of "a by-path" [11] In 2016, the IAU organized a Working Group on Star Names (WGSN)[12] to catalog and standardize proper names for stars. The WGSN approved the name Fulu for Zeta Cassiopeiae on 30 June 2017 and it is now so included in the List of IAU-approved Star Names.[9]


Cassiopeia starfield

Zeta Cassiopeiae is a B2 subgiant, indicating that it has exhausted its core hydrogen and started to evolve away from the main sequence. It has a temperature of over 20,000 K, is about eight times the mass of the sun, and is 5,500 times as luminous.


Zeta Cassiopeiae is a probable member of an unusual group of variable stars known as "Slowly Pulsating B" (SPB) stars.[13] It shows a pulsation frequency of 0.64 per day (or once every 1.56 days) and displays a weak magnetic field with a strength of roughly 3.35 × 10−2 T, which varies with a period of 5.37 days.[14] This likely matches the rotation rate of the star, which, when combined with the low projected rotational velocity, indicates the star may be seen nearly pole-on. Zeta Cassiopeiae is a candidate magnetic Bp star that shows an overabundance of helium. The star contains a randomly oriented fossil magnetic field, which impacts the outflow of the stellar wind. Collisions between streams from this stellar wind creates a shock front, with cooling particles settling toward a co-rotating disk.[15]


  1. ^ a b c d e van Leeuwen, F. (November 2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics, 474 (2): 653–664, arXiv:0708.1752, Bibcode:2007A&A...474..653V, doi:10.1051/0004-6361:20078357
  2. ^ Ducati, J. R. (2002). "VizieR Online Data Catalog: Catalogue of Stellar Photometry in Johnson's 11-color system". CDS/ADC Collection of Electronic Catalogues. 2237: 0. Bibcode:2002yCat.2237....0D.
  3. ^ a b c d e f g h i j Neiner, C.; Geers, V. C.; Henrichs, H. F.; Floquet, M.; Frémat, Y.; Hubert, A.-M.; Preuss, O.; Wiersema, K. (2003). "Discovery of a magnetic field in the Slowly Pulsating B star zeta Cassiopeiae". Astronomy and Astrophysics. 406 (3): 1019. Bibcode:2003A&A...406.1019N. doi:10.1051/0004-6361:20030742.
  4. ^ Morgan, W. W.; Keenan, P. C. (1973), "Spectral Classification", Annual Review of Astronomy and Astrophysics, 11: 29, Bibcode:1973ARA&A..11...29M, doi:10.1146/annurev.aa.11.090173.000333
  5. ^ a b Johnson, H. L.; et al. (1966), "UBVRIJKL photometry of the bright stars", Communications of the Lunar and Planetary Laboratory, 4 (99): 99, Bibcode:1966CoLPL...4...99J
  6. ^ Jaschek, C.; Gomez, A. E. (1998). "The absolute magnitude of the early type MK standards from HIPPARCOS parallaxes". Astronomy and Astrophysics. 330: 619. Bibcode:1998A&A...330..619J.
  7. ^ Gies, Douglas R.; Lambert, David L. (March 1992), "Carbon, nitrogen, and oxygen abundances in early B-type stars", Astrophysical Journal, Part 1, 387: 673–700, Bibcode:1992ApJ...387..673G, doi:10.1086/171116
  8. ^ a b "Zeta Cas -- Pulsating variable Star", SIMBAD, Centre de Données astronomiques de Strasbourg, retrieved 2010-02-22
  9. ^ a b "Naming Stars". IAU.org. Retrieved 16 December 2017.
  10. ^ (in Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 7 月 9 日
  11. ^ Richard Hinckley Allen: Star Names — Their Lore and Meaning: Cassiopeia
  12. ^ "IAU Working Group on Star Names (WGSN)". Retrieved 22 May 2016.
  13. ^ Neiner, C.; et al. (2003), "Discovery of a magnetic field in the Slowly Pulsating B star zeta Cassiopeiae", Astronomy and Astrophysics, 406 (3): 1019–1031, Bibcode:2003A&A...406.1019N, doi:10.1051/0004-6361:20030742
  14. ^ De Cat, P. (June 2007), "Observational Asteroseismology of slowly pulsating B stars", Communications in Astroseismology, 150: 167–174, Bibcode:2007CoAst.150..167D, doi:10.1553/cia150s167
  15. ^ Smith, M. A.; Bohlender, D. A. (May 2007), "Variations of the ultraviolet resonance lines of the B2 IV-V star ζ Cassiopeiae", Astronomy and Astrophysics, 466 (2): 675–682, arXiv:astro-ph/0702461, Bibcode:2007A&A...466..675S, doi:10.1051/0004-6361:20066639